The present invention relates to a protection circuit and a method for protecting a switching power supply system, and especially to a protection circuit arranged in a switching power supply system for protecting the switching power supply system.
FIG. 1 shows a protection circuit for a switching power supply according to prior art. Please refer to FIG. 1. A typical switching power supply system 1 utilizes a coupled feedback winding circuit 11 for powering the switching controller 2 of the switching power supply system 1. The switching controller 2 can be the industry standard 3842/3843 family of PWM controller. In case of an abnormal condition where the coupled feedback winding circuit 11 is unable to power the switching controller 2 (i.e. short circuit or overload on the output of the switching power supply system 1 or AC line voltage at a lower level), the switching controller 2 is shut down. However, the AC line voltage of the typical switching power supply system 1 keeps charging the capacitor 111 of the coupled feedback winding circuit 11 and thereby the switching controller 2 is unceasingly and alternately powered-on and powered-off
It is therefore attempted by the applicant to deal with the above situation encountered with the prior art.
It is therefore an object of the present invention to propose a protection circuit arranged in a switching power supply system for preventing the switching power supply system from being unceasingly and alternately powered-on and powered-off in an abnormal condition. The switching power supply system provides a supply voltage by using a coupled feedback winding circuit, and has a switching controller having a supply voltage terminal electrically connected to the coupled feedback winding circuit for being powered by the supply voltage. The protection circuit includes a detecting circuit electrically connected to the switching controller for providing a trigger signal when the supply voltage drops to an under-voltage level, and a latch circuit electrically connected to the detecting circuit for providing a latch signal to latch the switching power supply system when the detecting circuit provides the trigger signal to the latch circuit.
According to an aspect of the present invention, the detecting circuit is electrically connected to a reference voltage signal terminal of the switching controller.
Preferably, a reference voltage signal of the reference voltage signal terminal is at a low level when the supply voltage drops to the under-voltage level.
Preferably, the detecting circuit provides the trigger signal to the latch circuit for enabling the latch circuit to latch the switching controller, and causing an output of the switching controller to be set to zero.
Preferably, the detecting circuit includes a transistor having an emitter terminal electrically connected to the reference voltage signal terminal of the switching controller and a collector terminal electrically connected to one terminal of the latch circuit, a first diode having an anode end electrically connected to the reference voltage signal terminal of the switching controller and a cathode end electrically connected to a base terminal of the transistor, and a parallel circuit of a first resistor and a capacitor having one terminal electrically connected to the cathode end of the first diode, and the other terminal electrically connected to ground.
Preferably, the latch circuit has the other terminal for providing the latch signal to latch the switching controller.
Preferably, the detecting circuit includes a field effect transistor (FET) having an source terminal electrically connected to the reference voltage signal terminal of the switching controller and a drain terminal electrically connected to one end of the latch circuit, a first diode having an anode end electrically connected to the reference voltage signal terminal of the switching controller and a cathode end electrically connected to a gate terminal of the field effect transistor, and a parallel circuit of a first resistor and a capacitor having one terminal electrically connected to the cathode end of the first diode, and the other terminal of the parallel circuit electrically connected to ground.
It is therefore another object of the present invention to propose a protection circuit arranged in a switching power supply system for protecting the switching power supply system. The switching power supply system provides a supply voltage by using a coupled feedback winding circuit, and has a switching controller having a supply voltage terminal electrically connected to the coupled feedback winding circuit for being powered by the supply voltage. The protection circuit includes a detecting circuit electrically connected to the switching controller for providing a trigger signal when the supply voltage drops to an under-voltage level, and an auto-recovery protection circuit electrically connected to the detecting circuit for providing an auto-recovery protection to protect the switching power supply system when the detecting circuit provides the trigger signal to the auto-recovery protection circuit.
Preferably, the detecting circuit is electrically connected to a reference voltage signal terminal of the switching controller.
Preferably, a reference voltage signal of the reference voltage signal terminal of the switching controller is at a low level when the supply voltage drops to the under-voltage level.
Preferably, the detecting circuit provides the trigger signal to the auto-recovery protection circuit for enabling the switching power supply system shut-down and the auto-recovery protection circuit to auto-restart the switching power supply system after a restraint time.
Preferably, the detecting circuit includes a transistor having an emitter terminal electrically connected to the reference voltage signal terminal of the switching controller and a collector terminal electrically connected to one terminal of the auto-recovery protection circuit, a first diode having an anode end electrically connected to the reference voltage signal terminal of the switching controller and a cathode end electrically connected to a base terminal of the transistor, and a parallel circuit of a first resistor and a capacitor having one terminal electrically connected to the cathode end of the first diode, and the other terminal electrically connected to ground.
Preferably, the detecting circuit includes a field effect transistor (FET) having an source terminal electrically connected to the reference voltage signal terminal of the switching controller and a drain terminal electrically connected to one end of the auto-recovery protection circuit, a first diode having an anode end electrically connected to the reference voltage signal terminal of the switching controller and a cathode end electrically connected to a gate terminal of the field effect transistor, and a parallel circuit of a first resistor and a capacitor having one terminal electrically connected to the cathode end of the first diode, and the other terminal of the parallel circuit electrically connected to ground.
Preferably, the auto-recovery protection circuit includes a second resistor having one end electrically connected to the drain terminal of the field effect transistor and the other end of the second resistor electrically connected to the supply voltage terminal of the switching controller, and a second diode having a cathode end electrically connected to the drain terminal of the field effect transistor and having an anode end electrically connected to a duty-control feedback voltage terminal of the switching controller.
Preferably, a PWM output of the switching controller is set to zero when the duty-control feedback voltage terminal of the switching controller retained at a low level temporarily by the auto-recovery protection circuit.
Preferably, the restraint time is determined by the first resistor and the capacitor.
It is therefore another object of the present invention to propose a method for protecting a switching power supply system. The switching power supply system provides a supply voltage by using a coupled feedback winding circuit, and has a switching controller having a supply voltage terminal electrically connected to the coupled feedback winding circuit for being powered by the supply voltage and a reference voltage signal terminal Vref providing a reference voltage signal electrically connected to a detecting circuit. The method includes the steps of detecting that the reference voltage signal disappears when the supply voltage is smaller than a minimum of operating voltage and providing a trigger signal, and generating a latch signal to latch the switching power supply system in response to the trigger signal.
It is therefore another object of the present invention to propose a method for protecting a switching power supply system. The switching power supply system provides a supply voltage by using a coupled feedback winding circuit, and has a switching controller having a supply voltage terminal electrically connected to the coupled feedback winding circuit for being powered by the supply voltage and a reference voltage signal terminal providing a reference voltage signal electrically connected to an auto-recovery protection circuit. The method includes the steps of detecting that the reference voltage signal disappears when the supply voltage is smaller than a minimum of operating voltage and providing a trigger signal, and providing an auto-recovery protection to protect the switching power supply system in response to said trigger signal.
The present invention may best be understood through the following description with reference to the accompanying drawings, in which: